Limiting the peak-to-average power ratio in a mobile communication device during an uplink is desirable as the power efficiency of a power amplifier in a transmitter decreases with increasing peak-to-average power ratio. In a mobile communication device, where the power supply is typically limited, any reduction in power efficiency is undesirable. A power amplifier that requires a greater peak-to-average power ratio to operate effectively drains the power supply faster.
LTE systems, which use a LTE Single Carrier Frequency Division Multiple Access (SC-FDMA) uplink system, are becoming increasingly popular for use with mobile communication devices. It is thus often desirable to reduce the peak-to-average power ratio of such a system. 3rd Generation Partnership Project (3GPP) defines LTE as a mobile communications system that provides downlink peak rates of at least 100 megabits per second (Mbit/s), uplink peak rates of at least 50 Mbit/s, and radio access network (RAN) round-trip times of less than 10 milliseconds (ms). The terms uplink and downlink refer to transmission paths connecting two communication devices. An uplink refers to data being transmitted from the mobile communication device to a base station. A downlink refers to data being transmitted from the base station to the mobile communication device. LTE SC-FDMA is defined in the 3GPP specification for LTE.
LTE uplink systems use SC-FDMA, generally as SC-FDMA has a lower peak-to-average power ratio than other types of multiple access digital modulation schemes, such as Orthogonal Frequency Division Multiplexing Access (OFDMA). This lower peak-to-average power ratio is due to the inherent single carrier structure of LTE SC-FDMA. However, although LTE SC-FDMA generally has a lower peak-to-average power ratio, LTE transmitters tend to increase peak-to-average power ratio for a number of reasons. One such reason is the use of pulse shaping filters in the LTE transmitters. The pulse shaping filters are used to reduce out-of-band emission (OOBE), at the expense of causing an increase in peak-to-average power ratio.
It would be desirable to provide an effective suppression scheme in an LTE SC-FDMA system to reduce peak-to-average power ratio in conjunction with providing an efficient power amplifier for use in an LTE uplink system.